The purpose of this study was to determine the association of production factors with stayability to parity 4 (STAY 4), defined as the ability of a sow to reach 4th parity. Data was from the National Pork Producers Council Maternal Line National Genetic Evaluation Program, which included 6 genetic lines and consisted of 3,283 female pigs. Factors significant for STAY 4 included: farm, entry date, age at first farrowing, average daily gain, gilt backfat, and lactation prior to removal, feed intake, number born alive, and lactation length. Age at first farrowing and lactation feed intake in the lactation prior to removal had the greatest phenotypic relationships with sow longevity across genetic lines. A younger age at first farrowing under a uniform environment was positively related to length of productive life. Genetically, selection for a reduced age at first farrowing should increase sow longevity. However, a sow that is older at first farrowing may also be favorable for sow longevity. Commercial producers should strive to increase lactation feed intake through good management to ensure sow longevity.